Separation of hydrocarbons



Dec. 4, 1956 H.` E. CARVER Erm. 2,773,006

SEPARATION OF HYDROCRBONS Filed MaIQh 4, 1955 .cai-bons than is either procedure alone.

United States Patent- 2,773,006 SEPARATION F HYDROCARBONS Harold E. Carver, Brea, and George R. Lake, Long Beach, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application March 4, 1955, Serial No. 492,176

14 Claims. (Cl. 196-14.25)

This invention relates to methods for segregating hydrov carbon mixtures boiling over wide temperature ranges' into relatively aromatic, and relatively non-aromatic fractions. 'Iihe method embodies broadly a combination of selective solvent extraction of a high-boiling portion of the feed, and azeotropic distillation of the resulting extract with a lower-boiling portion of 'the feed. The rafinate from the extraction step is then combined with the hydrocarbon phase of the azeotropio overhead to form a relatively non-ar'omatic product. The bottoms from the aze-otropic distillation constitute the relatively aromatic product. It has been found that the combined procedure is capable of giving more efficient separation of the hydro- According to a preferred embodiment of the invention, a residual oil from a cracking operation boiling between about 400 yF. and 750 F., and containing between about 15% and 40% .by volume of aromatics, may be treated to produce a high grade diesel fuel in volume percent yields ranging between about 85% and 95%, and with an improvement in cetane number ranging between about 15% and 30%.

A broad object of the invention is to provide economical methods for segregating wide-range hydrocarbon mixtures into a highly aromatic portion and .a highly paranic and/or naphthenic portion. Another object is to provide methods for the solvent extraction of hydrocarbon oils with neutral organic solvents whereby the solvent may be recovered from the extract without the introduction of a third component, such as water, into the system. Another object is ,to combine the solvent recovery step with a hydrocarbon resolution step to effect simultaneous solvent recovery and hydrocarbon resolution. A specific object is to avoid the use of corrosive reagents such as sulfuric acid in the solvent treatment of hydrocarbons. Another specic object is to'provide methods for the treatment of low grade thermal or catalytic cracking cycle stocks for the removal of refractory aromatics, whereby the cetane number is improved and the product is rendered suitable fo-r use as diesel fuel. Other objects and advantages will be apparent from the more detailed description which follows.

One embodiment of the invention may be described briefly as follows in y connection with Figure l, which represents diagrammatically the hydrocarbon distribution at various stages in the process:

A- cracking cycle stock is indicated at A having a boiling range between about 420 F. and 660 F., and a boiling point distribution of aroma-tics and non-aromatics as indicated by the areas enclosed to the left of curves 1 and 2, respectively. In the first step of the process this oil is fractionated to recover a low-boiling side cut 3 and a high-boiling bottoms product 4. The bottoms' fraction should preferably amount to between about 30% and 70% by volume of the feed. The light ends 5 are taken overhead to be blended with the iinal diesel fuel product. The bottoms fraction 4 is then subjected to solvent extraction, employing a solvent which is selective for aromatics as compared to non-aromatics. Suitable solvents include,

- for example, phenyl cellosolve, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, dimethyl sulfolane, diethylene triamine, phenyl ethyl alcohol and the like. 'I'he solvent should preferably boil somewhere within theboiling range ofthe lowboilingside cut 3, and

p mainly of aromatic hydrocarbons.

. of the `aromatics capable of forming azeotropes.-

"ice

. 2- l should also be capable of forming azeotropes with parafns and naphthenes which boil within about 30 F. below and 70 F. above the boiling point of the solvent. Suitable solvents for hydrocarbon feeds of; other boiling ranges include for example isopropanol, butanol, nitromethane, aniline, phenol, morpholine, dioxane,` benzonitrile, n-itrobenzene andthe like. Mixtures of solvents may also be employed. 1

The compositionof .the raiinate from the solvent e traction is indicated at B, `and is mostly paratinic and naphthenic. The extract is mostly aromatic, on a solvent-free basis, as indicated qualitatively at C. The railinate B is blended with ,the nal diesel fuel product. The extract C is blended with the low boilingside cut 3, and

the whole is subjected to azeotropic distillation `at D toV the solvent-non-aromatic azeotropes, containing most of the non-aromatics from both extract C and side cut 3, may be taken overhead with only a minor proportionof the aromatics azeotropes. T-he major portion of .theyaromatics may be withdrawn, solvent-free,`as' bottoms by maintaining a bottoms cut-pointas indicated for example by the line 9.A A V It will be apparent that the quantity ofV aromaticsazeotropes taken overhead may be controlled to some extent by a proper selectionfof l,the boiling range of the side `cut 3. In some cases, the entire overhead portions 3 and 5 may be azeotroped with the extract Cf `In the case of very Wide-range feedshowever, transferring the 4over- `head portion 5 to azeotropic distillation D tends to vwiden undesirably the region of overlapping azeotropic boiling points for aromaticszand non-aromatics. It' is found desirable in the case of wide-range feeds to employ in the azeotropic distillation D a side-cut as illustrated, rather than the complete overhead fraction.V kIn such cases, an optimum side-.cut boiling range is obtainedby eliminating as overhead portion 5, a fraction having a boiling range which is between about 0.25 and 3 times the boiling range ofside-cut 3. v

The azeotropic distillation D is conducted in the presence of sufcient non-aromatics to azeotrope with at least themajor part and preferably all of the solvent, but insufficient solvent is present to form azeotropes with all This causes the aromatics to be continually displaced downwardly in the column, and a bottoms product may be withdrawn which is substantially solvent free, and consists The overhead from the azeotropic distillation is condensed, and since the nonaromatic hydrocarbons are relatively insoluble in the solvent a two-phase system is formed which may be readily separated by decantation. The hydrocarbon layer is then blended with the raiiinate B, and the overhea fraction 5 to form the nal diesel fuel product.

lt will be apparent from the above description that the process offers certain advantages over eithersolvent extraction alone, or -azeotropic distillation alone. Azeotropic distillation is impractical for recovery of the highboiling non-aromatics, because `the high temperatures encountered cause extensive decomposition of solvent capable of effectively azeotroping the high-boiling portions. If solvent extraction alone' is employed, there is considerable loss of non-aromatic hydrocarbons tothe extract.

Vcarbons to the extract.

,Theoptmumcombination .of solvent extraction of the high boiling portion of the. feed stock followed by azeotroping of the extract in the presence of a low boiling `portion of feedstock providessimultaneously for (l) recovery of the major part of the non-aromatics in the `extract, (2) recovery of solvent, and (3) the efficient segregation of aromatics `and non-aromatics of all boiling ranges. v

Many methods are known and practiced in the art #for segregating aromatic from non-aromatic hydrocarbons.v Perhaps the most generally used method consists -of solvent extraction with solvents which `are selective for aromatic hydrocarbons. Sulfuric acid, liquid sulfur dioxide, phenols, glycols and the Alike Vhave been employed forv thisy purpose. The use of sulfuric acid is disadvantageous because of corrosion problems, and because of .the diiiculty in recovering the acid for recycle, and because -the -aromatics and olens may be largely converted tojsulfonates which are sometimes undesirable. Liquid vsulfur dioxide is disadvantageous because of its poor selectivity and low solvent capacity, requiring the handling and recycle of large volumes lof solvent and high presvSure equipment. Any such solvent extraction methods valso result in considerable losses of non-aromatic hydro- Azeotropic distillation alone is Vrelatively ineifective for separating hydrocarbon mixtures which boil over a wide range, inasmuch as both the aroymatics andvnon-aromatics will generally azeotropewith the 4conventional solvents, and the boiling ranges of the' azeotropes will substantially overlap. It has been found in practice that the herein described combination of sol- "vent extraction and azeotropic distillation results in optimum liquid yields and efliciency When treating hydrocarbon mixtures boiling over a range of 80 F. or more. It has l been found especially useful for -treating high boiling stocks boiling within the range of about 400 F. to 750 F. for the production of diesel fuels. Such stocks should preferably have a major boiling point (temperature at which more of stock boils than at any other temperature) between about 460 F. and 560 F.

Cracked distillates boiling from -about 400 F. to 750 F., e. g. residual stocks from thermal or catalytic cracking units, usually contain about to 40 volume per cent `of aromatic hydrocarbons, nand this amount of aromatics lowers the cetane number below the minimum required fordiesel fuels.v The ignition quality ofy diesel fuels is measuredby the cetane number scale, a high cetane numbercorresponding to high ignition quality and a low cetanefnumber corresponding to a low ignition quality. Aromatic hydrocarbons, especially high boiling aromatics, are undesirable in diesel fuels because they have a low cetane number. High boiling n-paranson the otherhand are desirable constituents because they have a high cetane number. Naphthenic and oletinic hydrocar- .bOns are also desirable constituents. Other factors being equal, diesel fuel having a high proportion ofl aromatics vwould have a lower cetane number than a Afuel having Va low` proportion of aromatics. 1 According to the process .describedhereim sufficient aromatic hydrocarbons may be removedfrom high boiling cracked distillates to meet the minimum cetane number requirements, while maintaining liquid yields between 4about 85% and 95%. For example, feed stocks having an originalcetane number .of 33 may be treated to increase the cetane number to 40 at 87 volume percent yield. By sacrificing yield, the cetane number may be further raisedto, e. g. 60 to 65. Similarly, iflowercetane numbers are permissible, the yield may be increased to, e. g. 95

itg'will be apparent therefore that the invention is directed principally to the production of high quality diesel fuels from low quality cracked distillates. The basic prin- .ciples however may be applied to a wide variety of other mineral oil-distillates where it is desired to recover a highly aromatic, and/or a highly parainic or highly naphthenic fraction.

the lowest boiling naphthenes and parains.

Examples of other. feed stocks which may be treated include cracked gasolines, naphtha solvent fractions, kerosene fractions, light and heavy gas oils, and the like, any of which may be derived from petroleum, shale oil, tar sands, and the like. While removing aromatics, the process also removes a substantial portion of the organic sulfur and nitrogen compounds Which'may be present in the distillate.

Reference is now made to the accompanying Figure 2, which is a schematic flow sheet showing-the principal apparatus and steps which may be utilized for up-grading diesel stocks. This ow diagram will be explained specifically in reference to the treatment of a cycle stock from a catalytic cracking operation containing 34 volume percent of aromatics, having a cetane number of 33, and having Engler distillation characteristics somewhat as indicated at A of Figure l. This feed stock is introduced through line 12 into a distillation column 13. The light ends lof the stock boiling between about 420 F. and 460 F. are taken overhead through line 14. These light ends may amount to -about 5-25 volume percent of the stock, and may be blended with the nal diesel fuel product via line 16, or may be passed via line 16a to blend with the side-cut from line 15. A side-cut boiling` between about 460 F. and 510 F. (Z5-45 volume percent of the stock) is removed through line 15, and transferred via line 17 to azeotroping column 33 for use as described hereinafter. The approximately 50% bottoms product from column 13, boiling between about 510 F. and 730 F. is removed via line 18 and transferred to countercurrent solvent extraction column 20. Liquid solvent is introduced in the top of column 20 through line 21 and llows countercurrently downwardly, forming an aromatics-rich extract.

The raiiinate from column 20, corresponding approximately in composition as indicated at B of Figure l, but containing a small proportion of solvent, is withdrawn through line 22 and ,transferredto a small azeotroping column 23. In azeotroping column 23 the dissolved solvent is removed overhead in line 24 as an azeotrope with Thisv azeotrope is then condensed in condenser 25 and returned to line 21 for reuse in the extraction column. The solventfree bottoms from column 23 is removed via line 27, and blended with any overhead from line 16, the mixture comprising the product diesel oil in line 28.

The extract from extraction column 20 is withdrawn via line 30 and is blended with the side-cut or overhead from line 17. The mixture is then passed via line 31 into azeotroping column 33. In column 33 low boiling azeotropes are formed between the solvent and the naphthenes and paraflins from the column 13 side-cut, as well as the paraflins and naphthenes contained in the extract from column 20. The ratio of solvent to parans and naphthenes in column 33 should be adjusted so that sufficient parafiins and naphthenes are present to azeotrope substantially all of the solvent. This adjustment may be obtained by varying the solvent to feed ratio in column 20, by varying the volume of side-cut from column 13, and/ or by recycling a portion of the parain-naphthene fraction recovered as overhead from column 33. This recycle is admitted to the column via line 35. In order to remove solvent-free bottoms from column 33 it is also Vnecessary to maintain Vinsu'cient solvent to azeotropewith all of the aromatic hydrocarbons present. This factor is likewise adjusted by varying any of the above noted variables. The actual solvent/hydrocarbon ratio in column 33 will necessarily, depend upon the particular solvent employed, and the desired composition of overhead and bottoms. The lsolvent-free bottoms product from column 33, which is predominantly aromatic hydrocarbons is then withdrawn from line 37, and may be utilized for'the recovery of valuable aromatic hydrocarbons, or as fueluo'il. v

The azeotropic overhead from column 33 is withdrawn S through line 38, condensed in condenser 39 and transferred to a liquid-,liquid separator 40, wherein the solvent separates as the lower phase, and the non-aromatic hydrocarbons form the supernatant phase. It will be under- 6 It should be understood that the term "selective solventi as employed herein means that such solvent shall preferentially dissolve aromatic hydrocarbons in preference to either paraiiinic, naphthenic or oletinic hydrocarbons.

stood that the phase separation in separator 40` is essen- 5 The term selective aezotrope former means that the tially an added stage of solventA extraction, and hence solvent shall be capable of forming lower boilingv azeoeach phase will be saturated with all components. The tropes with parans, naphthenes, or olens of a particuhydrocarbon phase is saturated with solvent, amounting lar boiling point than is formed with aromatic hydroto about 0.2% to about 5.0% by volume. In orderto carbons having the same boiling point. It is also preremove the solvent this material is transferred via line 10 ferred that the selective azeotrope former should form 41to azeotroping column 23 wherein solvent is stripped azeotropes with parains, naphthenes and olens boiling overhead as azeotrope, along with rainate solvent `from over a wider range than the boiling range of aromatic extraction column 20. The combined solvent-free prodhydrocarbons which will azeotrope. uct is then withdrawn through line `27 and comprises the IThe solvent extraction step of this invention is carried mished diesel fuel product in line 28. out by the usual contacting procedures known in the art, The solvent phase in separator 40 may contain a small as for example by countercurrent extraction in a suitable amount of low boiling `aromatics. ln some cases, this column which may or may not be packed with granular proportion is negligible, as for example when the side-cut material such as glass beads 0r the like. The temperafrom column 13is a very narrow boiling cut, and hence tures ordinarily employed are about atmospheric, e. g. substantially no aromatics are azeotroped overhead in 50 F. to 100 F., although in somecases as for example column 33. In the case illustrated however, provision Where the solvent is viscous at low temperatures, elevated is made for removing at least a part of the dissolved temperatures up to about 300 F. may be employed. aromatics, in order to prevent the build-up thereof in the The solvent/feed ratios employed usually range between system. To accomplish this, the solvent phasein sepaabout 0.5 to 10 4by volume, and the equivalent of about rator 40 is withdrawn through line 42,` and a slip stream 25 l to l0 theoretical extraction `stages is ordinarily thereof is passed via line 43 into a small azeotroping employed. column 44, from which a solvent-aromatic azeotrope is The azeotropic distillation step is likewise conducted withdrawn through line 45. This small portion of azeoaccording to known general methods. The solvent extract trope may be diverted through line 46, and treated in any plus the low boiling feed fraction may be introduced desired manner for separating the solvent from the arosimultaneously near the mid-portion of a bubble cap matic hydrocarbons. For example, a small water washing column having a conventional reboiler, condenser and column may be employed. Alternatively, it may be rereux line. The solvent/feed ratios ordinarily range beazeotroped with low-boiling paratlns or naphthenes, e. g. tween about l and 10, but this factor should be adjusted a portion of the light ends in line 16, to recover overhead as pointed out above in order to provide in the column a solventparain azeotrope which may be recycled to sufficient non-aromatics to form azeotropes with subline 42, and as bottoms, substantially solvent-free arostantially all` of the solvent, but insufficient solvent to form matic hydrocarbons. Preferably however, the solventazeotropes with all of the aromatics capable of forming aromatics azeotrope is passed via line 47 and line 41 to azeotropes. Reliux ratios ranging between ab0ut2 and 30 azeotroping column 23, wherein the solvent content is may be employed, but it` has been found that little recovered overhead as azeotrope with low boiling paraf "#0 advantage is usually obtained by employing `reflux ratios fins, and the small residue of aromatic hydrocarbons is higher than about 8. The distillation is ordinarily conallowed to pass into the product via line 27. ducted at atmospheric pressures, but reduced pressures The bottoms from column 44 consists of hydrocarbonmay be employed if desired, from about 50ito 700 mm. free solvent which is returned via line 49 to the main v The following examples are cited to illustratethe critisolvent recycle line 42. The proportion of solvent which 4i cal features of the invention, but such examples should is diverted to azeotroping column 44 is again a matter of not be construed as limiting in scope. choice, and any desired portion may be treated, depending upon the proportion of aromatics which may be per- EXAMPLE I mitted at equilibrium in the process. The combined sol- Vent in line 42 is then recycled to line 21 for reuse in 50 This example illustrates the results obtainable by sol- Xtractifm column M i vent extraction alone. The feed stock employed was a Obviously many variations may be made in the procracked furnace oil obtained as residue from a catalytic cedure above described, and the invention should not be Cracking Operation The feed Steek hed a boiling fange construed as limited thereto. Any solvent may be ern- 0f about 434 F- t0 730 Fw a Peeifle gravity Of 60 F- ployed which (l) boils approximately within the boiling of 0.898, and other characteristics as indicated in Table range of the overhead or side-cut fraction whichis em- 1- This feed Steek Was Subleeted t0 Slllgle Stage batch ployed in the azeotropic distillation step, and (2) is a extfaetlel empleyllg the Solvents and PFOPOIODS noted selective solvent for aromatics, and (3) is a selective in Table I- The lallate from Cach CXIQCOD WaS azeotrope former for parains and naphthenes. Suitable analyzed for aromatics and non-aromatics. The results examples of such solvents have been mentioned above. @D were as follows:

Table 1 Ratnate Composition, Vol. Percent Vol. Vol. Raflnate Solvent Percent Percent Octane Solvent Non- Yield No. 1

Aro- Aromatics `Solvent 1 matics Phenyl Cellosolve 73. 7 20. 7 5. 6 67 47.

D0 300 86. 6 13. 4 o 54 55. 7 Dipropylene glycol 300 76.7 20.1 3.2 61 4&5 Dimethyl su1fo1ane 300 86. 4 9. 6 4. o 48 58. 5 Feed 53. 0 34. 1 33A 0 1 Solvent-free basis.

arr-3,1566

` The above data shows that all of the solvents employed effect a,. substantial improvement in cetane nurnber. and also remove a large proportion of the original aromatics. It will be noted, however, that the yield in all. cases; is low and hence solvent extraction alone is undesirable.

EXAMPLE Il This example illustrates the separation efficiency obtainable by azeotroping alone. The feed stock was the same residual oil employed in Example I, but was first fractionated into an overhead -50% fraction, boiling from about 460 F. to 524 F. and a 50-100% bottoms fraction boiling between about 574 F. to 727 F. Portions of the overhead fraction were then subjected to azeotropicv distillation with phenyl cellosolve and diethylene glycol, the high-boiling fraction not being amenable to azeotropic distillation.

A. In thedistillation with phenyl cellosolve 100 volumes ofthe 0-50% fraction were distilled with about 250 volumes of solventat a 20/1 reflux ratio. The azeotropic overhead was condensed and collected until the condensate became a. single solvent phase. The total two-phase condensate had a solvent/oil ratio of 1.14, and the oilrich phase contained 62.8% by volume of the charge oil, and was 65.7 volume percent paraflins plus naphthenes on a solvent-free basis, as compared to 51 volume percent for the .original 050% fraction.

rl`he oil-rich phase was then water-washed to remove solvent, and blended with 100 volumes of the 50-100% fraction of the original feed. The blend contained 36.4 volume percent of the azeotropic overhead, and 'had a cetane number of 39.5. The overall yield based on 200 volumes of the original feed, was 81.3 volume percent showing an unfavorable (cf. Example III) yield-cetane relationship for azeotroping alone followed by re-blending.

The azeotroping step was repeated at a /1 reflux ratio,l and the results were substantially the same, showing vthat high reflux ratios are not necessary to obtain optimum benefits from azeotroping the 0-50% fraction.

B. In the azeotroping with diethylene glycol, 100 volumes of the 0-50% fraction were distilled with about 200 volumes of the solvent at a /1 reflux ratio, and the two-phase azeotropic overhead collected as described above. The total two-phase distillate had a solvent/oil ratio of 0.95, and the oil-rich phase contained 95.1% by volume of the charge oil, and was 53.8 volume percent paraflins plus naphthenes on a solvent-free basis, as compared to 5l volume percent for the original 0-50% fraction. j

VThe oil-rich phase was then water-washed to remove diethylene glycol, and blended with 100 volumes of the 50-l00% fraction of the original feed. The blend contained 48.7 volume percent of the azeotropic overhead and lhad a cetane number of 35. The overall yield, based on 200 volumes of the original feed, was 97.5%, but the very small increase in cetane number outweighs the advantage of high yield.

EXAMPLE lll This example is cited to compare the efficiency of the combined process With the results obtainable by other combinations of azeotroping and solvent extraction.

Step ].-The initial feed stock was a residue oil from a catalytic cracking operation, having a cetane number of 33, and containing 53% by volume of acid-insoluble hydrocarbons (paraffins plus naphthenes). lts boiling range was 420 F. to 730 F. and its specific gravity was 0.898. This feed stock was first subjected to fractional distillation to obtain a 050% overhead portion boiling between about 420 F. and 508 F., and a 50-l00% bottomsl fraction boiling from508 F. to 660 F. The overhead fractionvcontained about 51'volume percent of acid-insoluble hydrocarbons, and the bottoms fraction contained about 58% of acid-insolubles.

vStep 2.-Tl1e overhead product from the above distillation was divided into `two equal portions. The first portion was subjected to azeotropic distillation with phenyl cellosolve at a solvent/oil ratio of 1.41, and a reflux ratio of 5/1. The azeotropic overhead was condensed and phase-separated to give a supernatant hydrocarbon-rich phase which contained 71% parains and naphthenes on a solvent-free basis, and amounted to 58.7 volume percent of the feed. The yield in this case was unsatisfactory.

Step SK-The bottoms fraction from distillation Step 1 was divided into two equalportions, the first portion was subjected to two-stage solvent extraction with the solventrich phase of the azeotropic overhead from Step 2. The overall solvent oil ratio was 0.86. The hydrocarbons in the raffinate oil from this extraction were found to contain 71 volume percent of parafiins and naphthenes, and the recovery was 87.1 volume percent, based on the portion of high-boiling feed thereto, but neglecting the hydrocarbon content of the solvent employed therein. It will be noted that the yield of this raflinate is fairly good if the original hydrocarbon content of the solvent is neglected, but the increase in non-aromatics is only about half that obtained in Step l. Moreover, the aromatics content was 22%, as compared to 25.5% for the feed.

Step 4,-The second portion of the overhead fraction from Step 1 was then subjected to azeotropic distillation in admixture with the extract from Step 3 above. The total solvent/oil ratio was 0.883, and the reflux ratio was 5/1. The` overhead fraction was condensed and subjected to phase separation to recover a supernatant hydrocarbon-rich layer, and a lower solvent-rich layer. The hydrocarbon-rich layer contained about 68 volume per cent paraf'lins and naphthenes, on a solvent-free basis, and the recovery was 68.7 volume per cent of the feed, based on the overhead portion taken from Step l.

Step 5.-The second portion of the bottoms fraction obtained in Step 1 was then subjected to two-stage solvent extraction employing as solvent the solvent-rich layer of the azeotropic overhead from Step 4. The overall solvent/ oil ratio was 0.667. The raffinate from this extraction was found to contain 67.3% by volume of paraffins and naphthenes, on a solvent-free basis, and the recovery was 93.3%, based on the bottoms portion taken from Step l.

Step 6.-The hydrocarbon layer from azeotropic distillation Step 2 and the raffinate from extraction Step 3 were then subjected to water washing to remove traces of solvent, and the two portions were blended. This blend contained about 69 volume per cent of paraffins and naphthenes, and had a cetane number of 46. The combined recovery was 73.4 volume per cent, based on 50% of the overhead and 50% of the bottoms fraction from Step 1. This fraction is high in cetane value but the total recovery is economically undesirable.

Step 7.-The hydrocarbon layer from azeotropic distillation Step 4, and the raffinate from extraction Step 5 were then Washed with water to remove traces of solvent and the two portions were blended. The final blend contained 67 volume per cent of parafiins and naphthenes, and had a cetane number of 45. The total volume per cent yield was 81.1%, based on 50% of the overhead and 50% of the bottoms fraction from Step l. This combined stream represents the optimum combination of cetane number and yield which the various combinations of azeotroping and extraction under the specific processing conditions produced. It will be noted that this blend is (1) the combined raffinate from a solvent extraction step employing a solvent-rich layer from an azeotroping step v as solvent, plus (2) the hydrocarbon layer of an azeotropic overhead resulting from the azeotroping of a cornbined high-boiling bottoms extract and the primary distillation overhead. This blend is considered to represent a typical yieldcetane relationship obtained in continuous equilibrium operation of the process.

It will be apparent, however, that higher cetane numbers may be obtained at the expense of yield by adjusting several process variables, e. g. increasing the proportion of solvent in the process, taking a lower boiling cut from the azeotroping step, etc. Likewise, higher yieldsrnay be obtained at the expense of cetane number by reversing such adjustments.

In all of the above azeotroping steps, it is found that substantially 100% of the solvent may be recovered overhead from the azeotroping column.1` However, in cases where the solvent/ oil ratio is inadequate to provide Vcomplete solvent recovery, a part of the hydrocarbon-rich phase from the overhead may be continuously recycled in the solvent. Alternatively, any traces of solvent remaining in the bottoms fraction may be recovered by adding a small proportion of low-boiling paraiiins and/ or naphthones, and azeotroping out the solvent as azeotrope with 'the added non-aromatic hydrocarbons.

Those skilled in the art will appreciate that the details of the above described procedures may be varied considerably to obtain the same ends. The description should therefore not be construed as limiting in scope in the abscence of explicit statements to that elect. The true scope of the invention is intended to be embraced by the following claim:

We claim:

l. A process for segregating a hydrocarbon oil containing aromatic and non-aromatic hydrocarbons boiling over the same temperature range of at least about 80 F. into a relatively aromatic portion and a relatively non-aromatic portion, which comprises fractionally distilling said oil to recover (l) a bottoms fraction amounting to between about 30% and 70% by volume of the feed oil, and (2) a lower-boiling fraction amounting to the major part of the total feed oil'boiling below said bottoms fraction; subjecting said bottoms fraction to solvent extraction with a solvent which (l) is a selective solvent for aromatics, (2) isa selective azeotrope former for non-aromatics, andl (3) boils approximately within the boiling range of said lower-boiling fraction of feed; recovering from said extraction a hydrocarbon ratiinate which is relatively nonarom'atic and an extract which contains a relatively aromatic hydrocarbon solute; subjecting said extract plus said lower-boiling fraction to mutual azeotropic distillation, recovering from said azeotropic distillation a bottoms fraction which is relatively rich in aromatic hydrocarbons, and an azeotropic overhead of solvent plus relatively nonaromatic hydrocarbons; separating the solvent from said azeotropic overhead and combining said relatively nonaromatic hydrocarbons from said azeotropic overhead with said relatively non-aromatic hydrocarbon raflinate.

2. A process as defined in claim l wherein the solvent/ oil ratio in said azeotropic distillation step is adjusted to provide sucient solvent to azeotrope with substantially all the non-aromatic hydrocarbons present and capable of forming azeotropes with said solvent, but insufficient to form azeotropes with all the aromatic hydrocarbons present and capable of forming azeotropes with said solvent, whereby the bottoms fraction from said azeotropic distillation is substantially solvent-free.

3. A process as defined in claim 1 wherein said hydrocarbon oil is a cracked mineral oil distillate having an initial boiling point between about 350 F. and 450 F., and end boiling point between about 650 F. and 800 F., and a major boiling point between about 460 F. and 560 F.

4. A process as defined in claim 3 wherein the solvent employed is a glycol mono-ether.

5. A process as defined in claim 3 wherein the solvent employed is a polyalkylene glycol.

, order to provide suicient non-aromatics to recover all 6. A process as dened in claim 3 whereinthe solvent employed is diethylene glycol. f

7. A process as deined in claim 3 wherein the solvent employed is dipropylene glycol.

8. A process as defined in claim 3 wherein the solvent employed is phenyl cellosolve. 'i

9. A process as defined in claim 3 wherein the solvent employed is dimethyl sulfolane.

10. A process for increasing the cetane number of a cracked `mineral oil distillate obtained as residue from a cracking operation, said distillate containing between about 15% and 40% by volume of aromatic hydrocarbons, and having an initial .boiling point between about 350 F. and 450 F. and an end-boiling point between about 650 F. and 800 F., which comprises fractionating said distillate to recover (l) a bottoms fraction amounting to between about 30% and 70% by volume of the `feed oil, (2) an adjacent lower-boiling side-cut fraction amounting to the major part of the total feed oil boiling below said bottoms fraction, and (3) a lirst overhead fraction boiling lower than said side-cut and having a boiling range between about 0.25 and 3 times the boiling range of said side cut; subjecting said bottoms fraction to solvent extraction with a solvent which (l) is a selective solvent for aromatics, (2) is a selective azeotrope former for non-aroma tics, and (3) boils approximately within the boiling range of said side-cut fraction of feed; recovering from said extraction a hydrocarbon rafiinate which is relatively nonaromatic and an extract which contains a relatively aromatic hydrocarbon solute; subjecting said extract plus said side-cut fraction to mutual azeotropic distillation, recovering from said azeotropic distillation a bottoms fraction which is relatively rich in aromatic hydrocarbons, and an azeotropic overhead of solvent plus relatively non-aromatic hydrocarbons; separating the solvent from said azeotropic overhead and combining said relatively non-aromatic hydrocarbons from said azeotropic overhead with said relatively non-aromatic hydrocarbon railinate and said rst overhead fraction to obtain a diesel fuel of improved cetane number.

l1. A process as dened in claim 10 wherein the solvent/ oil ratio in said azeotropic distillation step is adjusted to provide suicient solvent to azeotrope with substantially all the non-aromatic hydrocarbons present and capable of forming azeotropes with said solvent, but insuicient to form azeotropes with all the aromatic hydrocarbons present 'and :capable of forming azeotropes with said solvent, whereby the bottoms fraction from said azeotropic distil lation is substantially solvent-free.

12. A process as defined in claim 10 wherein said bottoms from said fractionation amounts to about 50 volume percent of the feed oil, said side-cut fraction amounts to between about 25% and 45% by volume of the feed oil,

and said overhead fraction amounts to between about 5% and 25 of the feed oil.

13. A process for segregating a hydrocarbon oil containing between about 15% and 40% by volume of aromatic hydrocarbons and between about 85% and 60% of non-aromatic hydrocarbons, each of said hydrocarbon classes boiling over the same temperature range of at least F., into a relatively aromatic portion and a relatively non-aromatic portion, which comprises fractionating said distillate to recover (1) a bottoms fraction amounting to between about 30% and 70% by volume of the feed oil, 2) an adjacent lower-boiling side-cut fraction amounting to the major part of the total feed oil boiling below said bottoms fraction, and (3) an overhead fraction boiling lower than said side-cut and having a boiling range between about 0.25 and 3 times the boiling range of said side-cut; subjecting said bottoms fraction to solvent extraction with a solvent which (1) is a selective solvent for aromatics, (2) is a selective azeotrope former for nonaromatics, and (3) boils approximately within the boiling range of said side-cut fraction of feed; recovering from said extraction a hydrocarbon rallinate which is relatively nonr aromatic and an extract which contains a relatively aromatic hydrocarbon solute; subjecting said extract plus said side-cut fraction to mutual azeotropic distillation; recovering `from said azeotropic distillation a bottoms fraction which is relatively rich in aromatic hydrocarbons, and an azeotropic overhead of solvent plus relatively non-aromatic hydrocarbons; separating the solvent from said azeotropicoverhead and combining said relatively non-aromatic hydrocarbons from said azeotropic overhead with said relatively non-aromatic hydrocarbon raffinate.

14. A process as defined in claim 13 wherein the solvent/oil ratio in said azeotropic distillation step is ad- .sufcient to form azeotropes with all the aromatic hydrocarbons present and capable of forming azeotropes with said solvent, whereby the bottoms fraction from said azeotropic distillation is substantially solvent-free.

References Cited in the le of this patent UNITED STATES PATENTS Roelfserna June 29, 1937 Poffenberger June 21, 1955 

1. A PROCESS FOR SEGREGATING A HYDROCARBON OIL CONTAINING AROMATIC AND NON-AROMATIC HYDROCARBONS BOILING OVER THE SAME TEMPERATURE RANGE OF AT LEAST ABOUT 80* F. INTO A RELATIVELY AROMATIC PORTION AND A RELATIVELY NON-AROMATIC PORTION, WHICH COMPRISES FRACTIONALLY DISTILLING SAID OIL TO RECOVER (1) A BOTTOMS FRACTION AMOUNTING TO BETWEEN ABOUT 30% AND 70% BY VOLUME OF THE FEED OIL, AND (2) A LOWER-BOILING FRACTION AMOUNTING TO THE MAJOR PART OF THE TOTAL FEED OIL BOILING BELOW SAID BOTTOMS FRACTION; SUBJECTING SAID BOTTOMS FRACTION TO SOLVENT EXTRACTION WITH A SOLVENT WHICH (1) IS A SELECTIVE SOLVENT FOR AROMATICS, (2) IS A SELECTIVE AZEOTROPE FORMER FOR NON-AROMATICS, AND (3) BOILS APPROXIMATELY WITHIN THE BOILING RANGE OF SAID LOWER-BOILING FRACTION OF FEED; RECOVERING FROM SAID EXTRACTION A HYDROCARBOBN RAFFINATE WHICH IS RELATIVELY NONAROMATIC AND AN EXTRACT WHICH CONTAINS A RELATIVELY AROMATIC HYDROCARBON SOLUTE; SUBJECTING SAID EXTRACT PLUS SAID LOWER-BOILING FRACTION TO MUTUAL AZEOTROPIC DISTILLATION RECOVERING FROM SAID AZEOTROPIC DISTILLATION A BOTTOMS FRACTION WHICH IS RELATIVELY RICH IN AROMATIC HYDROCARBONS, AND AN AZEOTROPIC OVERHEAD OF SOLVENT PLUS RELATIVELY NONAROMATIC HYDROCARBONS; SEPARATING THE SOLVENT FROM SAID AROMATIC OVERHEAD AND COMBINING SAID RELATIVELY NONAROMATIC HYDROCARBONS FROM SAID AZEOTROPIC OVERHEAD WITH SAID RELATIVELY NON-AROMATIC HYDROCARBON RAFFINATE. 